Fixed tab index order for tab press

[zubairshakoorarbisoft]

Description

On Discussion page, Post filters that are not pre selected are not keyboard accessible has been fixed inside learners and All Posts tabs.
Taiga Ticket: https://tree.taiga.io/project/zaraahmed-tutor-indigo-accessibility/us/27

How Has This Been Tested?

It has been audited by Accessibility team (Alina Naqvi)

I forked the repo from openedx and mount it and tested changes by making the fixes on local.

Screenshots/sandbox (optional):

Include a link to the sandbox for design changes or screenshot for before and after. Remove this section if it's not applicable.

Before	After

Merge Checklist

• If your update includes visual changes, have they been reviewed by a designer? Send them a link to the Sandbox, if applicable.
• Is there adequate test coverage for your changes?

Post-merge Checklist

• Deploy the changes to prod after verifying on stage or ask @openedx/edx-infinity to do it.
• 🎉 🙌 Celebrate! Thanks for your contribution.